1. Field of Invention
The present invention relates to an exhaust gas recirculation diagnosis device and an exhaust gas recirculation diagnosis method. More particularly, the present invention relates to an exhaust gas recirculation diagnosis device and exhaust gas recirculation diagnosis method using a MAP (manifold absolute pressure) sensor.
2. Description of Related Art
A large amount of harmful components such as CO, HC, and NOx (nitrogen oxides) is included in exhaust gas of an engine. Particularly, a high combustion temperature of the engine increases NOx generation, and therefore it is necessary to reduce the combustion temperature of the engine so as to reduce the NOx of the exhaust gas.
One main factor causing the combustion temperature of the engine to be raised is that the faster the spread of fire in a condition in which the density of the fuel mixture in a combustion chamber is high, the higher the temperature is, thereby raising the combustion temperature of the engine.
There is an exhaust gas recirculation (EGR) method that reduces the combustion temperature of the engine so as to reduce the NOx amount of the exhaust gas, wherein some of the exhaust gas is recirculated to the combustion chamber through intake air to deteriorate the density of the air/fuel mixture without changing the air/fuel ratio of the mixture, and therefore the combustion temperature of the engine is dropped.
The exhaust gas recirculation method reduces the NOx amount of the exhaust gas and improves fuel consumption efficiency of the engine. The use of the exhaust gas recirculation method reduces the temperature of the combustion chamber to reduce the NOx amount and simultaneously advances the ignition timing to avoiding knocking. Accordingly, engine output is improved and the fuel consumption efficiency is improved.
In the exhaust gas recirculation method, an EGR valve is used to control the amount of recirculated exhaust gas. If the EGR valve is fixed in an opened state, or is fixed in a closed state, the exhaust gas is not normally recirculated. If the EGR valve is fixed in an opened state, engine output is deteriorated and an engine surge can be generated. If the EGR valve is fixed in a closed state, the exhaust gas is not supplied to the combustion chamber, the combustion chamber temperature is not reduced, and the engine output is not improved. In addition, the exhaust gas can be abnormally recirculated by various causes such as a fault of a vacuum hose or a solenoid valve operating the EGR valve.
If the exhaust gas is not normally recirculated because of a fault of the exhaust gas recirculation device, the engine generates exhaust gas including a large amount of NOx. Therefore, it is necessary to diagnose the fault of the exhaust gas recirculation device and inform a driver of the fault.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.